Synthesis and characterization of compatibilized poly(epsilon-caprolactone)/granular starch composites

To improve the mechanical properties of granular com starch-filled poly(eps ilon -caprolactone) (PCL) compositions, three strategies were investigated including the hydrophobic coating of starch granules by reaction with n-but yl isocyanate, the addition of PCL-grafted dextran (PGD) as an amphiphilic compatibilizer, and the use of PCL-grafted granular starch (PGS). Except fo r the chemical modification of granular starch by reaction with n-butyl iso cyanate, the synthesis of both PGD and PGS relies upon the controlled ring- opening polymerization (ROP) of epsilon -caprolactone (CL) initiated by Al- alkoxides generated onto the polysaccharide, either dextran or starch parti cles. While the hydrophobic coating of starch only provides higher tensile strength and elongation at break, these properties as well as Young's modul us and strength at yield of the PCL/starch blends were remarkably increased by locating the PCL-grafted dextran at the filler/matrix interface. It is however worth pointing out that a tougher and stiffer material was obtained by melt blending PGS and pure PCL. These property changes were analyzed an d clearly related to parameters such as filler dispersion, interfacial tens ion, interfacial adhesion and reinforcement by PCL crystallites.